More than 20 million Americans on average use marijuana each month, making it the most popular street drug in the country. Four states -- Oregon, Washington, Colorado, and Alaska --and the District of Columbia have legalized recreational marijuana. Many other states are considering laws to make it legal.

The number of Americans who are in favor of legalizing recreational marijuana has risen. More than half of people surveyed now support the idea. Most Americans don't think marijuana is harmful. Yet despite the increasing acceptance, marijuana use does have some risks.

Here's a look at how marijuana can affect your health.

How does marijuana work on the brain?

When you smoke or eat marijuana, chemicals called cannabinoids are released into your body. The main cannabinoid is THC.

Cannabinoids move from your lungs or stomach into your blood. From there, they travel to your brain and the rest of your body. THC acts on certain receptors in your brain. This creates the "high" some people feel.

Marijuana vs. Alcohol

Is marijuana safer than alcohol, or vice versa? Each substance has different effects on the body. Here's how the two compare. In most cases, these effects have been studied in heavy, chronic smokers and drinkers, not occasional users.